Appending files to an archive

To append files to an archive, you'll use one of the following functions
from File_Archive class:

appender
(
$URL
, $unique = null
, $type = null
, $stat = array()
)

Allows to append to the archive specified by the URL.

If unique is set to true, the eventual duplicates
created by the insertion of new files will be automatically removed.
If set to null, the default value
(that you can change using
File_Archive::setOption('appendRemoveDuplicates', true/false))
is used (false by default).

If the archive does not exist, it will be created using the type
specified in parameter
(or looking at the extension in the URL if the type is not specified),
and the stat array.